This invention is directed to environmentally friendly solvents, and particularly to cleaning, rinsing, and drying agents which are binary azeotropic or azeotrope-like compositions containing a volatile methyl siloxane (VMS).
Since local, state, federal, and international regulations, have restricted the use of some chemicals, a search is on for replacement solvents. VMS have been found to be one suitable solvent replacement. The Environmental Protection Agency (EPA) has determined that volatile methyl siloxanes such as octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, hexamethyldisiloxane, octamethyltrisiloxane, and decamethyltetrasiloxane, are acceptable substitutes for CFC-113, the chlorofluorocarbon (C.sub.2 Cl.sub.3 F.sub.3), and methylchloroform (MCF). This is limited to closed systems for metal cleaning, electronic cleaning, and precision cleaning applications, under their Significant New Alternatives Policy (SNAP).
In addition, EPA has excluded VMS as a volatile organic compound (VOC). The EPA added VMS to the list of compounds in 40 CFR 51.100(s) excluded from the definition of VOC, on the basis that VMS compounds have negligible contribution to tropospheric ozone formation. They pointed out that exempting VMS from regulation as ozone precursors contributes to the achievement of several important environmental goals, and that VMS might be used as a substitute for several compounds listed as hazardous air pollutants (HAP). As they explained, that met the need to develop substitutes for ozone depleting substances (ODS) and attained National Ambient Air Quality Standards for ozone under Title I of the Clean Air Act.
Compounds designated VMS by EPA exemption are cyclic, branched, or linear, "completely methylated" siloxanes. "Completely methylated" means that methyl groups and no other functional groups are attached to the central backbone of the siloxane.
Volatile methyl siloxanes have an atmospheric lifetime of 10-30 days and do not contribute significantly to global warming. They have no potential to deplete stratospheric ozone due to short atmospheric lifetimes, so they do not rise and accumulate in the stratosphere. VMS contain no chlorine or bromine atoms; they do not attack the ozone layer; they do not contribute to tropospheric ozone formation (Smog); and they have minimum GLOBAL WARMING potential. VMS are hence unique in simultaneously possessing these attributes. It should be apparent that VMS provide one positive solution to the problem of finding new solvent replacements.